The present invention relates in general to a regulating valve suitable for controlling the flow of a fluid in response to a sensed condition, and more particularly, to such a regulating valve suitable for controlling the flow of a heating or cooling medium in response to changes in temperature at a selected location, which temperature changes are sensed by a thermal element, and designed to either permit or prevent flow of the heating or cooling medium upon failure of the thermal element.
Regulating valves are commonly used for controlling the flow of a heating or cooling medium internally within a surrounding jacket of, for example, engines, compressors, heat transfer equipment and the like. The temperature of the heating or cooling medium in the jacket is sensed by a thermal element. These thermal elements are typically of the expansion type incorporating liquid, vapor, gas, wax or bi-metallic members to produce the necessary force and movement. In heating operations, the flow of the heating medium is increased when the sensed temperature drops and reduced when the sensed temperature increases. On the other hand, in cooling operations, the flow of the cooling medium is reduced when the sensed temperature drops and increased when the sensed temperature increases.
In a typical situation where cooling water or brine is supplied to the jacket of an internal combustion engine or a compressor, the fluid in the thermal element expands and elongates a bellows assembly in response to an increase in the temperature of the cooling water or brine flowing through the jacket. The elongated bellows is operative to extend a shaft to move a pilot mechanism in a preferred direction to cause the regulating valve to open and increase the flow of cooling water or brine to the jacket. On the other hand, a drop in temperature of the cooling water or brine causes the collapse of the bellows assembly and the retraction of the shaft. This results in the pilot mechanism moving in another preferred direction to cause the regulating valve to close, to a varied degree, thereby reducing the flow of the cooling water or brine until the temperature of same within the jacket to the engine returns to within the desired range.
In the foregoing situation, failure of the thermal element corresponds to the thermal element sensing an extremely low temperature which results in the collapse of the bellows assembly and the retraction of the shaft. This results in the pilot mechanism moving to a position which closes off the flow of the cooling water or brine to the jacket, despite the fact that the temperature of the cooling water or brine within the jacket may be excessively high. As a consequence, there is a serious potential to cause irreparable damage to the engine. This problem is also present when using a heating medium such as oil or steam in heat transfer equipment such as reaction vessels and the like. The failure of the thermal element will accordingly correspond to the sensing of a very low temperature which, in turn, causes the pilot mechanism to move to a position to open the flow of hot oil or steam to the jacket of the reactor vessel. As a consequence, the chemical reaction may be adversely effected with potentially dangerous consequences.
In order to overcome the foregoing problem resulting from the failure of the thermal element, complex circuits and auxiliary controls have been devised to provide what has been commonly referred to as a fail-safe type action. In addition, thermal elements have been constructed by being filled under vacuum so that their filled normal working length is shorter than their relaxed or unfilled length. Although these alternative designs perform the desired function, they are often complex and expensive, limited in application range, less reliable than the standard known thermal elements, more vulnerable to hostile conditions, and often not readily available as stocked items.